The present invention relates in general to fluid separation centrifuges which are designed to separate particulate matter from a fluid which circulates through the centrifuge. More specifically, the present invention relates to a disposable centrifuge rotor with an internal seal. The internal seal is provided in order to help retain collected soot and ultra-fine particles of 0.01 to 1.0 microns in size in the intended collection zone.
While the present invention is believed to have broad applicability to disposable centrifuge rotors, it is described in the context of two specific centrifugal rotor designs. One design selected is a current product of Fleetguard, Inc. of Nashville, Tenn., offered under part number CS41000. The other design is a split-flow centrifuge.
The current CS41000 centrifuge rotor was designed to have a base plate that mates to an inner ring on the inside of the bottom rotor housing. The mating interfit between the parts creates a circumferential line-to-line contact. With this design, the CS41000 product demonstrates excellent performance for the collection of dust in the size range of 3 to 80 microns. However, it was learned that the performance of the CS41000 centrifugal rotor was not as efficient for soot collection for particulate in the size range of 0.01 to 1.0 microns. This change in performance was ultimately attributed to a pressure gradient and fluid leakage between the base plate and rotor housing.
Analysis of the flow and separation efficiency of centrifuges, by means of computational fluid dynamics (CFD) modeling software, applied to various centrifuge designs, indicated that a substantial pressure gradient existed across the base plate. It was concluded that this substantial pressure gradient in turn caused a leakage flow between the rotor housing and the base plate at their circumferential interface (i.e., contact) location. It was thought that the substantial pressure gradient caused some deflection in the base plate that contributed to the leakage flow across this interface location.
In order to further analyze the nature of the flow and the effects of leakage at the rotor housing-base plate interface, a split-flow centrifuge was selected and modified to have a predefined 0.5 mm gap. It was learned that the flow actually becomes reversed from the desired condition. More specifically, it was learned that the xe2x80x9cdriving fluidxe2x80x9d (exiting from a bottom port on the shaft), which is supposed to stay below the base plate and go directly to the jet nozzle outlets, is actually re-routed up through spiral vane outlet holes where only the xe2x80x9cthrough-flowxe2x80x9d portion (from a top port on the shaft) is supposed to be exiting. Both the through-flow and driving fluid then pass through the xe2x80x9cleakxe2x80x9d annulus before proceeding to the jet nozzle outlets. This leakage, and more specifically the associated flow, causes a large increase in the degree of fluid motion, especially in the critical area near the outer wall of the rotor housing which is designed as the sludge/soot collection zone for the rotor. This increased fluid motion causes some of the separated soot to be xe2x80x9cwashed outxe2x80x9d of the collection zone, a result which is highly undesirable. The problem increases in severity as rotor speed increases. The amount of separated sludge (or soot) from that residing in the collection zone which is then re-entrained into the flow depends in part on the degree of leakage at the rotor housing-base plate interface.
In order to address this concern, the present invention was conceived and reduced to practice as a working model. Testing with the working model confirmed the viability and value of the present invention as a way to address the aforementioned problem of leakage at the rotor housing-base plate interface.
Prior to arriving at the present invention, a number of sealants were tried as a way to fix the leakage problem. However, the large pressure gradient which is experienced by the base plate caused the base plate to deflect and this pulled the sealant loose and opened a leakage path.
The present invention creates a cylindrical surface-to-cylindrical surface contact between the base plate and the bottom portion of the rotor housing. In one embodiment this surface contact is achieved by the addition of a U-clip lip on the outer peripheral edge of the base plate. This inverted U-clip lip interlocks with an upwardly extending cylindrical projection which is integral with the rotor housing. This interlocking relationship, by an interference fit, ensures that the base plate does not experience any deflections which are sufficient to open up a fluid leakage path. In other embodiment, this surface contact is achieved by adding an upwardly extending cylindrical wall on the outer peripheral edge of the base plate. The same upwardly extending cylindrical projection of the rotor housing is used. The cylindrical wall and the cylindrical projection are in tight contact and spin welded together into a sealed interface. For the first embodiment using the U-clip, the present invention can also accept the use of a sealant such as one of the anaerobic compounds or a silicon-based material for an even more robust seal, if desired.
A separation centrifuge for the separation of particulate matter from a fluid according to one embodiment of the present invention includes a rotor housing and a fluid separation device positioned within the rotor housing wherein the improvement comprises a base plate as part of the fluid separation device which is designed and arranged with a peripheral lip which is formed with a generally cylindrical modified portion therein. A generally cylindrical projection as part of the rotor housing is designed and arranged to contact the modified portion so as to create a generally cylindrical sealed interface at the location of circumferential contact between the projection and the modified portion.
One object of the present invention is to provide an improved rotor assembly for a fluid separation centrifuge.
Related objects and advantages of the present invention will be apparent from the following description.